GETHOSTBYNAME(3)          386BSD Programmer's Manual          GETHOSTBYNAME(3)

NAME
     gethostbyname, gethostbyaddr, gethostent, sethostent, endhostent, herror
     - get network host entry

SYNOPSIS
     #include <netdb.h>
     extern struct h_errno;

     struct hostent *
     gethostbyname(char *name)

     struct hostent *
     gethostbyaddr(char *addr, int len, int type)

     struct hostent *
     gethostent(void)

     sethostent(int stayopen)

     endhostent(void)

     herror(char *string)

DESCRIPTION
     The gethostbyname() and gethostbyaddr() functions each return a pointer
     to an object with the following structure describing an internet host
     referenced by name or by address, respectively.  This structure contains
     either the information obtained from the name server, named(8),  or
     broken-out fields from a line in /etc/hosts. If the local name server is
     not running these routines do a lookup in /etc/hosts.

     struct  hostent {
             char    *h_name;        /* official name of host */
             char    **h_aliases;    /* alias list */
             int     h_addrtype;     /* host address type */
             int     h_length;       /* length of address */
             char    **h_addr_list;  /* list of addresses from name server */
     };
     #define h_addr  h_addr_list[0]  /* address, for backward compatibility */

     The members of this structure are:

     h_name       Official name of the host.

     h_aliases    A zero terminated array of alternate names for the host.

     h_addrtype   The type of address being returned; currently always
                  AF_INET.

     h_length     The length, in bytes, of the address.

     h_addr_list  A zero terminated array of network addresses for the host.
                  Host addresses are returned in network byte order.

     h_addr       The first address in h_addr_list; this is for backward
                  compatiblity.

                  When using the nameserver, gethostbyname() will search for
                  the named host in the current domain and its parents unless
                  the name ends in a dot.  If the name contains no dot, and if
                  the environment variable ``HOSTALIASES'' contains the name
                  of an alias file, the alias file will first be searched for
                  an alias matching the input name.  See hostname(7) for the
                  domain search procedure and the alias file format.

                  The sethostent() function may be used to request the use of
                  a connected TCP socket for queries.  If the stayopen flag is
                  non-zero, this sets the option to send all queries to the
                  name server using TCP and to retain the connection after
                  each call to gethostbyname() or gethostbyaddr().  Otherwise,
                  queries are performed using UDP datagrams.

                  The endhostent() function closes the TCP connection.

FILES
     /etc/hosts

DIAGNOSTICS
     Error return status from gethostbyname() and gethostbyaddr() is indicated
     by return of a null pointer.  The external integer h_errno may then be
     checked to see whether this is a temporary failure or an invalid or
     unknown host.  The routine herror() can be used to print an error message
     describing the failure.  If its argument string is non-NULL, it is
     printed, followed by a colon and a space.  The error message is printed
     with a trailing newline.

     The variable h_errno can have the following values:

     HOST_NOT_FOUND  No such host is known.

     TRY_AGAIN       This is usually a temporary error and means that the
                     local server did not receive a response from an
                     authoritative server.  A retry at some later time may
                     succeed.

     NO_RECOVERY     Some unexpected server failure was encountered.  This is
                     a non-recoverable error.

     NO_DATA         The requested name is valid but does not have an IP
                     address; this is not a temporary error.  This means that
                     the name is known to the name server but there is no
                     address associated with this name.  Another type of
                     request to the name server using this domain name will
                     result in an answer; for example, a mail-forwarder may be
                     registered for this domain.

SEE ALSO
     resolver(3),  hosts(5),  hostname(7),  named(8)

CAVEAT
     The gethostent() function is defined, and sethostent() and endhostent()
     are redefined, when libc(3) is built to use only the routines to lookup
     in /etc/hosts and not the name server.

     The gethostent() function reads the next line of /etc/hosts, opening the
     file if necessary.

     The sethostent() function is redefined to open and rewind the file.  If
     the stayopen argument is non-zero, the hosts data base will not be closed
     after each call to gethostbyname() or gethostbyaddr().  The endhostent()
     function is redefined to close the file.

HISTORY
     The herror() function appeared in 4.3BSD. The endhostent(),
     gethostbyaddr(), gethostbyname(), gethostent(), and sethostent()
     functions appeared in 4.2BSD.

BUGS
     These functions use static data storage; if the data is needed for future
     use, it should be copied before any subsequent calls overwrite it.  Only
     the Internet address format is currently understood.

4.2 Berkeley Distribution        July 31, 1991                               3